This invention relates to a liquid crystal display device, and more particularly to a display device including a super twisted nematic liquid crystal composition wherein the liquid crystal includes a compound having a terminal --CN or --F radical.
Conventional super twisted nematic (STN) type liquid crystal display devices are often utilized in liquid crystal display devices in personal computers. However, these conventional display devices have slow response times. Thus, computers equipped with these display devices are not fast enough to support a peripheral device, such as a mouse.
The following relationship exists between response time (t), viscosity (.eta.) and the thickness of the liquid crystal layer (d): EQU t.varies..eta.d.sup.2
In order to decrease the response time (t) and quicken the response, it is necessary to decrease the viscosity of the liquid crystal composition or the thickness of the liquid crystal layer. When the display device is driven at a duty ratio of 1/200, it is possible to achieve a response time of 150 msec or less if d is 5.5 .mu.m or less. If a response time of 100 msec or less is desired, d should be about 4 .mu.m or less.
As the thickness of the liquid crystal layer is decreased, irregularities, commonly referred to as cross-talk, conspicuously appear along scan electrode lines and signal electrode lines of the liquid crystal display device. These irregularities are the result of different contrasts in nonselective modes.
Cross-talk increases as a result of an increase in the capacitance of the liquid crystal layer. In other words, cross-talk is caused by the rounding of waveform of voltage applied to the liquid crystal and spike shaped noises. The level of cross-talk depends on the scale of the rounding or the noise. As the capacitance of the liquid crystal layer increases, the rounding and the noise increases. The capacitance of the liquid crystal layer also increases as the thickness of the liquid crystal decreases. Thus, as the response speed increases, the capacitance increases and cross-talk increases, resulting in an inferior liquid crystal display device.
Accordingly, it is desirable to provide a liquid crystal display device which does not suffer from the shortcomings of the prior art and which has a fast response, reduced cross-talk and no flicker of the display.